The structure and location of Drosophila contractile protein genes is under investigation. These genes appear to be activated in muscle cells in culture at the point when myoblasts fuse to form multinucleate myotubes. Utilizing recombinant DNA techniques, we are constructing bacterial clones containing cDNA copies of these gene sequences. Once identified, cloned DNAs will be used to map the location of contractile protein genes on polytene chromosomes. These clones will also be utilized to obtain genomic DNA fragments which can then be analyzed and compared by restriction mapping, heteroduplex formation and DNA sequencing. We thereby intend to search for DNA sequences that are required for coordinated regulation of this gene set during cellular differentiation.